Time delay device



p 16, 1958 R. w. DE LANCEY 2,852,640

' TIME DELAY DEVICE Filed Oct. 6, 1955 .1 El. T q /74 53 ATTORNEY States TIME DELAY DEVICE Ralph W. DeLanccy, Des Plaines, Ill., assignor, by mesne assignments, to Controls Company of America, Schiller Park, Ill., a corporation of Delaware Original application August 10, 1954, Serial No. 448,966.

Divided and this application October 6, 1955, Serial No. 538,883.

1 Claim. (Cl. 200-422) In many electrically operated devices, the requirement often exists for the operation of two or more of the components in a predetermined order. One such application is the conventional oil burner wherein it is desirable to initiate the delivery of air into a combustion chamber before the admission of oil and to halt the admission of oil when the demand for heat has been satisfied and before the supply of 'air is interrupted. While this method of operating an oil burner is extremely desirable in order toeliminate smoke and materially retard the accumulation of carbon and soot on the internal areas of the furnace, the relative highcost and complication of controls for the attainment of this end has prohibited their general use in average oil burner installations.

Accordingly one object of the invention resides in the provision of an improved time delay control incorporating at least two time delay devices that may be used to control one or two circuits and characterized by its simplicity, dependability and low cost.

Another object of the invention is an improved heat responsive switch assembly including an associated heater wherein the switch is automatically compensated for changes in ambient temperature and the switch and heater may be used to control two independent circuits in a predetermined manner and with a high degree of stability and dependability.

Still another object of the invention is an improved thermal time delay control device.

The accompanying drawings show, for purposes of illustrating the present invention, an embodiment in which the invention may take form, it being understood that the drawings are illustrative of the invention rather than limiting the same.

In the drawings:

Figure 1 is a perspective view of one embodiment of a switch in accordance with the invention;

Figure 2 is a cross sectional View of the embodiment of Figure 1 taken along the line 22 thereof; and

Figure 3 is a circuit diagram illustrating an application of the switch of Figure l in oil burner installations.

Referring now to the drawings and more specifically to Figures 1 and 2, the switch 53 embodies a pair of temperature compensated bimetallic elements and a negative temperature coeflicient resistor. The control devices of the switch are mounted on and carried by an angle .bracket 171 having a mounting leg 172 and a switch supporting leg 173. The contacts 85 and 86 for controlling one circuit are carried respectively by a strip 174 preferably bimetallic, and a leaf spring 175 of Phosphor bronze or the like. Movement of contact 86 and spring 175 is effected by an L-shaped bimetallic element 176 heated by a negative temperature coefficient resistor 90. A heat baflie 178 is disposed between the bimetal element 174 and contact spring 175 to shield the element 174 from the heat generated by resistor 90 when the latter functions to heat the element 176 and cause contacts and 86 to close.

The elements of this switch are held in predetermine spaced relationship by a plurality of insulating spacers 179 to 186 and a pair of screws 187 extending through insulating bushings'188 and threaded into a plate 189 on the back side of the mounting bracket 171. In order to prevent damage to insulator 186, metal plates 190 and 191 may be interposed between the heads of screws 187 and insulator 186 as illustrated.

The negative temperature coefficient resistor is held in close proximity to the bimetallic element 176 by a pair of fiat electrically conductive spring members 192 and 193 having terminals 192? and 193, respectively, for connection to a circuit. The member 193 includes a cup-like part 194 for retention of resistor 90. The contact carrying members 174 and also terminate in terminals 1'74"and 175 for connection to an electric circuit. The member 175 is sprung backwardly to rest against and follow the movement of the bimetallic element 176. Both bimetallic elements 176 and 174 are arranged to move in the same direction with changes in ambient temperature so that the spacing between contacts 85 and 86 normally remains the same. Upon heating, element 176 shifts relatively to the element 174 to close the contacts. The spacing between contacts 85 and 86 is adjustable by means of a screw 195 threaded in a cooperating opening in bracket part 173 and bearing against the plate 196 which in turn lies against the root end of the bimetallic contact carrying member 174.

The switch as described above embodies means for ambient temperature correction, adjustment of the contacts to vary the time delay in opening and a negative temperature coefiicient resistor that may be used to control the operation of an external circuit as well as heating the bimetallic elements. For instance, this resistor may be used to provide delayed operation of an oil valve in oil burning equipment and the bimetallic switch to delay interruption of the blower motor on the burner after the demand for heat has been satisfied. This application is illustrated in Figure 3. In this figure M denotes the blower motor of an oil burner connected to a suitable source of energy- 80 through a switch 81 that may be the switch used in conventional oil burner installations. Thus when there is a demand for heat switch 81 will close to start motor. At the same time switch 82 is closed to energize the oil controlling means'represented by the valve V through the negative temperature coefiicient resistor 90. The nominal or cold temperature resistance of resistor 90 is relatively high and will prevent sutficient flow of current to operate the valve. Thus upon starting only the blower motor M will function. Since the resistor 90 decreases in value as it heats in response to the current flowing through it, its resistance will fall, after a predetermined time interval to a value that will operate valve V and supply oil to the burner. In this way oil is not fed to the burner until an adequate supply of air is being furnished by the blower.

In addition to delaying admission of oil to the burner, the heater 90 also heats the bimetallic element 176 and causes contacts 85 and 86 to close and bypass the motor control switch 81.

After the demand for heat has been satisfied, both switches 81 and 82 are automatically opened. This will immediately de-energize valve V to stop the supply of 3 oil but inasmuch as contacts 85 and 86 are closed the motor M will continue to supply air for an interval of time determined by the rate of cooling of the bimetallic elements 174 and 176. In this way the motor M is started prior to the admission of oil and continues to run for a time after the oil supply is interrupted.

From the above it is apparent that the switch may be used to control other devices required to function in a predetermined sequence or the resistor 90 and contacts 85 and 86 can be connected with a device to be controlled so that a time delay is interposed on both starting and stopping the controlled device.

While only one embodiment of the invention has been illustrated and described it is apparent that modifications, changes and alterations may be made without departing from the true scope and spirit thereof.

What is claimed is:

A temperature responsive switch comprising a first bimetallic element fixedly mounted at one end, a contact carried on the other end thereof, a second contact and a flexible mount therefor positioned for cooperation with the said first contact, a second bimetallic element associated with and controlling the position of said second contact, said second bimetallic element being arranged to move in the same direction as said first element and maintain substantially uniform contact spacing with 4 changes in ambient tempertaure, a heat baflle between the first bimetallic element and the support for said second contact and a heater including a negative temperature coeflicient resistor associated with said second bimetallic element for heating it relative to the first element to actuate said contacts. 7

References Cited in the file of this patent UNITED STATES PATENTS 1,562,932 Walker Nov. 24, 1925 1,871,875 Bradford Aug. 16, 1932 1,898,174 Dubilier Feb. 21, 1933 1,948,938 Lawton Feb. 27, 1934 1,960,408 Brach May 29, 1934 2,110,690 Zierahn Mar. 8, 1938 2,235,337 Shaw Mar. 18, 1941 2,248,623 Hand July 8, 1941 2,303,153 Woodworth Nov. 24, 1942 2,341,905 Cook Feb. 15, 1944 2,499,906 Crise Mar. 7, 1950 2,535,969 Tramontini Dec. 26, 1950 2,563,341 Kettering Aug. 7, 1951 2,605,308 Grine July 29, 1952 2,689,288 Wells Sept. 14, 1954 

